1. Field of the Invention
The invention relates to an optical communication device, and more particularly to a compact optical transceiver integrated module.
2. Description of the Related Art
A laser module with a beam wavelength of about 1.3 xcexcm which is used for a subscriber terminal of a broad-band optical communication network, is required to have a transmission rate of about 155 Mbps. This type of laser module is widely utilized in a terminal system, i.e., the broad-band network and the optical cable TV system, etc. An optical transmitter module converts an electric input signal to an optical signal of 1.3 xcexcm wavelength, whereas an optical receiver module converts an optical signal to an electrical signal.
The optical transmitter module of 1.3 xcexcm beam wavelength modulates light emitted from the front section of a laser diode into an electric signal and then connects the modulated electric signal to an optical fiber. The connected light or signal is transferred through the optical fiber, and the light transmitted along the optical fiber is converted back to electrical signal at the other end of the optical receiver module.
In general, the above optical transmitter and receiver modules are integrated in a packaging arrangement with at least 20 pins, and connectors are fabricated to be fitted as receptacles in use thereof. Most packaging arrangements used today includes at least 20 pins that are fabricated with metal metals, thus each of the 20 pins needs a complete electric isolation from the optical subassembly. Hence, the manufacturing process becomes very complicated. As the metal packaging arrangement is costly, a plastic packaging has been developed lately to reduce the production cost. In addition, as most optical transmitter and receiver modules being used today have optical fibers attached thereto thus making them inconvenient during the handling process, receptacle type optical transmitter modules without the optical fibers are gaining interest.
A compact packaging arrangement, which has been proposed in the early 1998, is about half size of the previously used optical transceiver integrated module, thus can be mounted with two times of integrity in the same area. Moreover, the compact packaging arrangement has advantages in that it can be applied to various types of connectors, such as MT-RJ connector, LC connector, etc.
A laser diode, which converts an electric signal into an optical signal and a photodiode, which converts an optical signal into an electric signal, are typically assembled using a metal packaging arrangement known as xe2x80x9cTO-can.xe2x80x9d There are disadvantages associated with the xe2x80x9cTO-canxe2x80x9d in that the fabrication process is expensive as the cost of the metal packaging tends to be high. Also, the process time for connecting the metal packaging and the optical fiber tends to be long. Furthermore, a very expensive laser welding equipment has to be used when using the xe2x80x9cTO-can.xe2x80x9d
Current optical transceiver integrated module uses a receptacle type packaging with 9 pins, and the laser diode and photodiode are contained within the metal package of the xe2x80x9cTO-can.xe2x80x9d Thus, a cap welder application is required to fabricate the xe2x80x9cTO-canxe2x80x9d packaging arrangement. However, the laser welder application is very costly, thus the cost of the optical transceiver is expensive.
The space from one section connected via a connector to another section for transmitting and receiving the optical signal is 0.75 mm in the MY-RJ package and 6.35 mm in the LC package, as specified in the standard. However, the space cannot be constructed by aligning the TO-can itself in parallel form. To this end, a specifically structured optic device is further required to reduce the light path between the TO-can and the connector.
As shown in FIG. 1, one illustrative example of arrangement for packaging optical communication arrangement includes a lens 11 and mirrors 12 and 13 used for reducing the light path. Here, a special technique is required to form the mirrors 12 and 13. Due to the construction of the resin optics 10, the single mode transmission is impossible since the coupling of the light with single mode optical fiber is a difficult task. Therefore, the optics 10, as shown in FIG. 1, cannot be used for a long distance communication but can be used only for a short distance communication using multi-mode optical fibers.
It is, therefore, an object of the invention to provide a technique for manufacturing a compact optical transceiver integrated module using a silicon optical bench, in which a novel plastic packaging arrangement is provided, instead of a metal package, using a silicon optical benching technique applied to manufacture the novel optical transceiver module; as a result, the packaging size is reduced to half when compared to the previous optical transceiver module and a simple process can be performed without using the expensive metal package or other devices, and an MT-RJ or LC connector complying with international standard can be used.
According to one aspect of the present invention, the compact module includes
a silicon optical bench having a laser diode subassembly and a photodetector subassembly integrated thereto, the laser diode subassembly including an optical signal transmitting laser diode, the the photodetector subassembly including an optical signal receiving photodetector;
a PCB circuit board for installing the silicon optical bench, the circuit board provided with a laser diode subassembly driving circuit and a photodetector subassembly driving circuit, the laser diode subassembly driving circuit applies an electrical signal to the laser diode subassembly to drive the same so that the optical signal is generated from the electric signal, and wherein the photodetector subassembly driving circuit converts the optical signal received by the photodetector into the electrical signal; and,
a plastic package for sealing the PCB circuit board so that the PCB circuit board may be isolated.
According to another aspect of the invention, the laser diode subassembly and photodetector subassembly are applied with a silicon gel, which is applied with an encapsulating agent to effectively prevent a moisture absorption from the outside, whereby active components provided on the silicon optical bench can be protected from an external environment change.
According to another aspect of the invention, the silicon optical bench is connected to an RJ-45 connector using a 2-core ferrule and the core distance of the optical fibers in the core ferrule is 0.75 mm.
According to another aspect of the invention, the silicon optical bench is connected to an RJ-45 connector using a set of an optical fiber/ferrule/sleeve arrangement and the core distance of the optical fibers is 6.35 mm.
According to another aspect of the invention, the laser diode mounted on the silicon optical bench and the optical fiber connected to the photodetector are manually aligned.
According to another aspect of the invention, the cover is composed of plastic.
According to another aspect of the invention, the compact module further includes a shielding case for shielding a pre-amplifier of the photodetector subassembly driving circuit and the receiver photodetector from an external EMI (Electro-Magnetic Interference), the shielding case being fixed to the PCB in the periphery of the pre-amplifier of the photodetector subassembly driving circuit and the receiver photodetector.
According to another aspect of the invention, the shielding case is provided with a double layer structure.